This invention relates to a structure in which a piezoelectric transformer element for use in a piezoelectric inverter of a backlight for a liquid crystal display or the like is mounted on a circuit board equipped with circuit components and a method of mounting the same.
As a conventional mounting method of a piezoelectric transformer element, there is known a mounting method in which the piezoelectric transformer element is contained in a case and an external terminal of the case is connected by soldering or the like to a circuit board equipped with a circuit component. Another mounting method is also known in which no casing is carried out to avoid a problem of heat generation following an increase in output power but a vibration node is fixed by the use of a flexible elastic material, for example, silicone.
In order to adjust the brightness of a backlight, it is required to carry out control of an inverter electrically connected to the backlight. As a circuit system for such brightness adjustment, a burst adjustment is generally used.
This results in a problem of generation of an audible sound, which has not been caused in the conventional method of fixedly supporting the piezoelectric transformer used in the inverter. The reason is as follows. The piezoelectric transformer is generally driven in a single mode. However, by addition of a brightness adjusting function, the piezoelectric transformer itself is driven in a mode other than the single mode. Even if the piezoelectric transformer is fixedly supported at a nodal point in the single mode, a nodal point in the other mode will be deviated from the supporting point. This results in generation of the audible sound in a mounted state.
Therefore, it is a first object of this invention to provide a mounting structure of a piezoelectric transformer element, which can minimize generation of an audible sound even if it is used in vibration modes of different frequencies.
It is a second object of this invention to provide a method of mounting the above-mentioned piezoelectric transformer element.
According to this invention, there is provided a mounting structure of a piezoelectric transformer element which is mounted on a circuit board equipped with at least one circuit component for driving the piezoelectric transformer element, wherein the piezoelectric transformer element is fixed to the circuit board by the use of at least one of a fixing member and a supporting member made of an elastic material having flexibility and interposed between the piezoelectric transformer element and the circuit board so as to cover vibration node portions of the piezoelectric transformer element and at least a part of a remaining portion except the vibration node portions.
According to this invention, there is also provided a mounting structure of a piezoelectric transformer element which is mounted on a circuit board equipped with at least one circuit component for driving the piezoelectric transformer element, wherein the circuit board is formed in a manner such that an area between portions corresponding to vibration node portions of the piezoelectric transformer element and outer areas outside of the above-mentioned portions are depressed comparing with the portions corresponding to the vibration node portions and that the length across the outer areas exceeds the length of the piezoelectric transformer element, the piezoelectric transformer element being fixed to the circuit board by the use of a fixing member made of an elastic material having flexibility and interposed between the piezoelectric transformer element and the circuit board at the vibration node portions of the piezoelectric transformer element.
According to this invention, there is also provided a mounting method of a piezoelectric transformer element which is mounted on a circuit board equipped with at least one circuit component for driving the piezoelectric transformer element, wherein the piezoelectric transformer element is fixed to the circuit board by the use of at least one of a fixing member and a supporting member made of an elastic material having flexibility and interposed between the piezoelectric transformer element and the circuit board so as to cover vibration node portions of the piezoelectric transformer element and at least a part of a remaining portion except the vibration node portions.
According to this invention, there is also provided a mounting method of a piezoelectric transformer element which is mounted on a circuit board equipped with at least one circuit component for driving the piezoelectric transformer element, wherein the circuit board is formed in a manner such that an area between portions corresponding to vibration node portions of the piezoelectric transformer element and outer areas outside of the above-mentioned portions are depressed comparing with the portions corresponding to the vibration node portions and that the length across the outer areas exceeds the length of the piezoelectric transformer element, the piezoelectric transformer element being fixed to the circuit board by the use of a fixing member made of an elastic material having flexibility and interposed between the piezoelectric transformer element and the circuit board at the vibration node portions of the piezoelectric transformer element.
Thus, in this invention, as a method of mounting a piezoelectric transformer element on a circuit board equipped with at least one circuit component for driving the piezoelectric transformer element, the piezoelectric transformer element is fixed at vibration nodes by the use of a flexible elastic material (preferably, silicone or the like). Furthermore, another flexible elastic material is inserted in a portion other than the vibration nodes in a spot-like fashion or in parallel to the vibration nodes to be used as a spacer. In this manner, the piezoelectric transformer has a structure hard to transmit the vibration to the circuit board upon excitation which is not a single mode excitation. Thus, it is possible to suppress a heat generation and an audible sound.